They’re America’s new Puritans.
It’s worth noting that the American Left are in fact the ideological descendants of the people who originally populated New England from old England. It’s why Massachusetts and the northeast in general are such a blue region. The primary difference is merely what they’re puritanical about.
Remember Mencken’s quip about Puritanism being “the haunting fear that someone, somewhere, may be happy”? William F. Buckley Jr. paraphrased this talking of Ralph Nader as an example of the New Puritanism, “the haunting fear that someone, somewhere, may be making a profit.” But now the NP’s have gone back to sex. Weird.
There is, I suspect, a religion-shaped hole in the human psyche, and nature abhors a vacuum.